The present invention relates to chest compression devices and in particular to a high frequency chest wall oscillator device.
In a variety of diseases such as cystic fibrosis, emphysema, asthma, and chronic bronchitis, the mucus that collects in the tracheobronchial passages is difficult to remove by coughing. This may be due to the characteristics of the mucus (such as its quantity or viscosity, or both), or because the patient does not have the strength or lung capacity to produce an adequate cough. Manual percussion techniques of chest physiotherapy are labor intensive, uncomfortable, and make the patient dependent on a care giver. As a result, devices and methods for airway clearance, such as the use of a chest compression device, have been developed.
A chest compression device useful for airway clearance should meet a number of criteria based on human factors, engineering, and common sense. First, it must be safe to operate. Second, it should provide some degree of user control. Third, it should be easy to understand and operate. Fourth, it should minimize the intrusion into the daily activities of the user. Fifth, the device should be highly reliable. Sixth, it should be of a design which does not result in unusual service requirements for the device. Seventh, the weight and bulk of the device should be reduced to a point that foreseeable users can maneuver the device. Eighth, the device must be able to provide adequate force over a relatively large surface area in an energy efficient manner so it can be operated from AC or battery.
A successful method of airway clearance makes use of high frequency chest wall oscillation (HFCWO). The device most widely used is the ABI Vest Airway Clearance System by American Biosystems, the assignee of the present application. The ABI Vest System is a pneumatically driven system, in which an air bladder is positioned around the chest of the patient and is connected to a source of air pulses. A description of this type of system can be found in the Van Brunt et al. patent, U.S. Pat. No. 5,769,797 which is assigned to American Biosystems.
Other chest compression devices have also been used or described in the past. For example, the Warwick et al. patent, U.S. Pat. No. 4,838,263 describes another pneumatically driven chest compression device. Mechanical vibrators and direct mechanical compression devices have also been used to produce high frequency chest wall oscillators.
In the pneumatic system described in the Van Brunt et al. patent, an air pulse generator is connected to the air bladder contained in a vest which is positioned around the chest of the patient. The air pulse generator provides a pulsed source of air in conjunction with an adjustable static source of air. The static air pressure acts as a xe2x80x9cbias linexe2x80x9d around which the pulses of air pressure from the pulse source are referenced. Thus, an increase in the static pressure has the effect of oscillating the chest wall with greater intensity despite the pressure change (Delta) of the pulsed waveform (max to min.) remaining constant.
Pneumatically driven HFCWO produces substantial transient increases in the airflow velocity with a small displacement of the chest cavity volume, increases in cough-like shear forces, and reductions in mucus viscosity resulting in a unidirectional increased upward motion of the mucus through the bronchioles.
The pneumatic system as disclosed in the Van Brunt et al. patent and as implemented in the ABI Vest System from American Biosystems has been a very successful and widely used method for airway clearance. The pneumatic system meets the first six requirements of a chest compression device, but could be improved with respect to bulk, weight, and energy efficiency.
The present invention is a chest wall oscillator device that performs the function of loosening and assisting in the removal of excess mucus from a person""s lungs. The chest wall oscillator includes a chest band having first and second ends for placement around a person""s chest, a drive unit connected to the chest band cyclically varies the circumference of the chest band to apply an oscillating compressive force to the chest of the person. The chest wall oscillator also includes a means for maintaining the oscillating compressive force applied by the chest band to the chest of the person at a substantially constant level such that the person is able to continue chest expansions and contractions as during regular breathing.
In preferred embodiments of the present invention, an air bladder is placed on the inner surface of the chest band for engaging the chest of the person and applying a xe2x80x9cbias linexe2x80x9d pressure to the person""s chest. The drive unit preferably includes a motor which is connected to the first end of the chest band and a linkage which is connected to the second end of the chest band. The linkage is driven by the motor to cyclically move the second end of the chest band relative to the first end of the chest band, thereby effectively varying the circumference of the chest band around the person""s chest and producing the oscillating compressive force.